MORPHOGENESIS OF THE CHOROID PLEXUSES 509 



Aiich hier wie bei Teleostiern bleiben die Plexus inferioris (median 

 telencephalic choroid plexus) nur in Gestalt einer Querfalte nach- 

 weisbar, die Paraphyse ist eine blosse Kuppel, der caudalen Rand wir 

 als rudinientares \'elum auffassen. 



There are no lateral telencephalic choroid plexuses in Cyclo- 

 stomes. 



Among the Selachians, ho^ve^"er, there is a well formed plexus 

 inferioris in Xotidanus according to Burckhardt ('94), but no 

 lateral telencephalic plexuses appear. On the other hand, I infer 

 from Kappers and Carpenter ('ID tliat in Chiniaera monstrosa 

 the lateral plexuses are present. 



Der ependyniale Theil der Sciiluszplatlc \V()ll»t sicli in ihiciii tVoiital- 

 sten Al)schnitt ctwas iiber deni Niveau des (ieliinies hiuaus cine Art 

 paraj)hyse darslt'ilciul uiu sicli daini plotzlieh wieder eiuzufalteii und 

 in den unparen X'entrikel eindrinjicnd den plexus chorioideus vent rieuli 

 imparis zu bildcn. wovon audi jicrinRe Auslaufci- in den schnialen 

 Seit(MiventriUe!n ilvt^ (lehirns eindrinjien. 



And Minot ('01) in dosciihing Acantliias lemarks: 



verA 



The velum has now distinctly the character of a choroid |ilcxus, beiu}!; 

 _ry irregular in the form of its surface, rich in blood vessels, covered 

 by a thin ependyma ami projecting far into the ca\'ity of the brain. 

 Laterally the projections from its surface are much more developed 

 and as the organ has grown forward alongside the median para])hysal 

 arch, it has produced what we can now easily identify as the jilexus of 

 the lateral ventricle. These i)lexuses are therefore to be interpicted 

 morphologically as scH'ondary modifications or appendages of the pri- 

 mary velum transversum Attention should be jiaid to the 



two lateral projections. L.ch., of the ependyma on the anterior sui-face 

 of the velum, because these j^rojections not only fix the lateral bound- 

 aries of the paraphysal arch but also are the anlages of the choroid 

 plexuses of the lateral ventricles. These anlages from this stage (28.0 

 mm.) on rapidly increase both in size and in comjilication of form. 



D'Erchia ('9(3) shows in Torpedo the velum transformed into 

 a plexus and the tela chorioidea diencephali practically non- 

 existent. In fact, this seems to be the tendency of these two 

 structures in the entire Selachian group. There is a i)lexus in 

 the roof of the fourth ventricle in all Selachians. 



No plexus develops in the tela chorioidea telencephali medii 

 in Ganoids, but in Acipenser, von Kupffer ('93) figures a plexus 

 formation arising from the anterior wall of the velum trans- 



